Electrostatic printing is a well known printing process in which an electrostatic latent image is made to attract electrostatic marking particles, that is, a toner. The toner can be of the dry type or of the liquid type. Electrostatic printing is particularly applicable when only a relatively small number of prints are required, or when the subject matter is frequently changed, or when part of the subject matter needs to be sequentially changed.
Dry powder toners have many disadvantages when used in such a process. The main objection is related to the dusting problem. Dust, or fine, or small particles of toner are prone to escape from the developer, and these deposit onto any surface both within and outside the printing device, causing mechanical failures within the device and environmental problems outside the device. This problem becomes severe when such printing devices are run at high speed. Other disadvantages include cost of the general maintenance of the press and cost of the dry powder toner.
Liquid electrostatic printing also has a number of objectionable problems, especially when these devices are required to operate at high speed. The main problem is in regard to the solvent carry-out. The term solvent carry-out relates to the quantity of solvent or carrier which is trapped within the paper and mechanically removed from the toner applicator. Such solvent subsequently evaporates, giving rise to atmospheric pollution and also adding significantly to production costs. A further disadvantage of liquid toning is the tendency for deposition of coloring matter in non-image or background areas which results in a general discoloration of the copy, normally referred to as background fog.
It has previously been found that in those instances in which the printing master consists of a ferroelectric recording member having a more or less permanent latent image impressed on or about its surface by way of internal polarization, the liquid dispersed toner may be caused to contact the printing master in the image areas only, thus eliminating background fog and substantially reducing solvent carry-out. This is disclosed in U.S. patent application Ser. No. 07/697,106, filed May 8, 1991, Staples et al.
The meniscus toning method of the referenced application Ser. No. 07/697,106 results in a substantial reduction in solvent carry-out and elimination of background fog under carefully controlled conditions.